<IMG SRC="http://www.google.com/images/logo.gif" ALT="This website rocks!">
This gives me this result (drag your mouse over it and hold it still for a few seconds):
The alternative text will also show up when the graphic isn't coded correctly like this:
<IMG SRC="http://www.google.com/images/logoarughaj.gif" ALT="This website rocks!">
That bad code gives me this:
As you can see, alternative text is very handy and a good way to manage images.
Also, if you can't get an image to come up, make sure you have http:// written at the beginning, not just www.!
NOTE FROM NILS: Some of the information shown above may not work on some browsers exactly as described. The information above is accurate for Internet Explorer, however.